1. Field of the Invention
The present invention relates to a two-way relay transmission apparatus and method, and more particularly, to a two-way relay transmission apparatus and method applied to multi-input multi-output (MIMO) communication systems.
2. Description of the Prior Art
Relay transmission is considered an important component in the continued evolution of wireless communication networks. Conventional half-duplex relay transmission can only perform one-way signal transmission or reception at any time and, therefore, requires 4 time slots to complete one bi-directional signal exchange in relay-assisted signal transmission between two terminals. In two-way relay transmission, the relay can receive from or transmit to two terminals simultaneously and therefore requires only 2 time slots to complete one bi-directional signal exchange in relay-assisted signal transmission, which can thus substantially improve the efficiency in spectrum utilization.
One conventional two-way relay transmission technique is the amplify-and-forward (AF) technique. However, it uses a greater-than-necessary “constellation” at the relay terminal. For example, consider the situation where both terminals employ Binary Phase Shift Keying (BPSK) with signal values 1 or −1, and the two terminal-to-relay channels both have unity gain. Then the received signal at the relay terminal may take one of three values: 0, 2 and −2. To maintain the same noise performance, the average transmission power needed for this ternary signal is twice that for BPSK, and the peak power is 4 times that for BPSK.
To sum up, how to reduce the peak and the average two-way relay transmission powers is an issue desiring solution.